I am trying to understand this. If the 12 volt battery under the hood starts the engine and powers the electric motor what does the 12 volt battery under the hood do?

 

It powers up the electronics until the system kicks in the big battery.

When an FEH 12V battery gets marginal, you can get a variety of very confusing and unintuitive symptoms. Luckily it's a quick & easy fix (replace the battery).

 

I just had the 12 volt battery tested at mechanic and they said it is good. I will drive it again tomorrow and see hiw it goes. If it shuts off again I will go to Ford.

 

Sometimes my relays fail to shut down after I shut off the engine. - -The next -time I try to start the vehicle, there is no power as if the 12V battery is dead. I -then hook up a power pack jump starter and one can hear the "wrrrr" closing of -the relays. I can then unhook the power pack- and start the vehicle as if nothing happened. This has never happened when I was driving.

 

I got the SSN warning on the fwy, thankfully in heavy traffic, so limped off and let it sit before restarting and making it home. I had the dealership get codes and one was for a 'low 12V' something or other, PLUS a lot of other odd codes that made no sense. I had my battery tested and it also 'passed', but I think at least one cell was marginal, it being 5yrs old, so I replaced it and never had the problem again. You should check the date code on the battery, and of course the cables just to ensure nothing has come loose. Above all else, ensure you have the dealership pull codes -- most generic code readers will NOT be able to pull Ford-specific codes.

 

I actually had the 12 volt battery replaced in November. Does the dealership usually charge to pull the codes?

 

The dealer I go to does charge a flat $125 diagnostic fee but they waive that if you have the repair done there. But since you didn't get any warning lights or messages, it might be a tough one to diagnose. Places like Autozone will usually hook up for free but it seems like it's rare that they actually find anything for the FEH.

 

I just realized that my car does not make the noises when I open the door anymore. Is this is the sounds that the car makes when it is checking the electrical system? Does anyone know what that may be?

 

I think that's the electrical booster pump for the brakes pressurizing.

 

The scanners Autozone uses are largely unable to read any of Ford's proprietary codes.